Palytoxin is one of the most poisonous substances in the animal kingdom, yet some of the creatures that produce it are housed in marine aquariums. How should this situation be handled?

Back in 2012 I read a very detailed and interesting article by Dr. Maik Friedrich, entitled Palytoxin—from the Aquarium to the Hospital? The author, a medical doctor and biologist, summarized the then astonishingly sparse scientific literature dealing with palytoxin poisoning in the aquarium hobby. Since then, however, a number of expert reports on the subject have appeared in scientific journals. Friedrich’s article interested and motivated me to such an extent that I co-authored a paper on the subject myself (Tartaglione et al. 2016b). See References below.

The paper, which appeared in the journal Toxicon, documented the first case of palytoxin poisoning in Italy. An aquarist from Bolzano in the South Tyrol had tried to remove a colony of Palythoa polyps from his reef tank by scrubbing them from the substrate rock with a brush under hot running water. During this procedure he breathed in the resulting vapor, and subsequent chemical analysis of the remaining Palythoa polyps from his aquarium isolated palytoxin and two additional palytoxins new to science: a hydrossypalytoxin and a desoxypalytoxin. The encrusting anemone was identified morphologically and genetically as Palythoa cf. toxica, and laboratory experiments demonstrated that aquarium-hobby activated carbon removed most of the palytoxin from the aquarium water.

The study was carried out by scientists from the Department of Pharmacy at the University of Naples Federico II, Italy; the Department of Life Sciences at the University of Trieste, Italy; the South Tyrol Museum of Natural History, Bolzano, Italy; the Molecular Invertebrate Systematics and Ecology Laboratory at the University of the Ryukyus, Okinawa, Japan; and the General Hospital of Bolzano.

In principle, humans can be exposed to the toxin in three different ways:

• Eating contaminated fish or crustacean products; this is the most dangerous form of palytoxin poisoning, though to date it has resulted in death only in the tropics, not in subtropical zones.

• Inhaling vapor containing palytoxin

• Eye or skin contact with encrusting anemones or their secretions or with contaminated sea water

In the last 10 years, and with increasing frequency, numerous cases of poisoning involving Palythoa species or unidentified encrusting anemones from marine aquariums have been documented in the scientific literature. The first documented case took place in Germany (Hoffmann et al. 2008): A 32-year-old aquarist removed encrusting anemones from his aquarium without wearing gloves and injured three fingers on his right hand in the process. He noticed the first symptoms two hours later: shivering, muscle pain, and a feeling of weakness. In the hours that followed his condition deteriorated and he was taken to the emergency department of a clinic. The minor injuries to his hand were inflamed and swollen, and before long his entire arm felt numb. An ECG showed changes indicating heart muscle damage. Two days later the patient was free of symptoms and was released. Investigation of the encrusting anemones from his aquarium showed a concentration of 2–3 mg palytoxin per gram (Mebs 2010).

Reports of palytoxin poisoning also appear regularly in aquarium-hobby magazines and on the Internet, although they are not usually confirmed by laboratory analysis. A very well-known case is that of Dietrich Stüber, who described the incident in an article (2010). Stüber was the first aquarist who was able to get an Acropora stony coral to grow in the aquarium, and he is regarded as one of the fathers of the Berlin reefkeeping method. He was seriously poisoned when he removed about 10 Palythoa polyps from his aquarium using long forceps, without taking his usual precautions (turning off the pumps and protein skimmer and wearing a protective breathing mask). At that time the Palythoa species had been living in his tank for more than 15 years. Two hours later he started to experience difficulty breathing and fits of coughing. His symptoms worsened rapidly and he was taken to a hospital.

On admission to the intensive care unit (ICU), Stüber was already unconscious. His condition was so critical that he was put into medically induced coma for three weeks. The diagnosis was acute respiratory distress, probably triggered by the inhalation of Palythoa toxin, with acute damage to the lungs. After two months in the ICU he was transferred to a rehabilitation clinic, where he spent several weeks. Following this mishap, Stüber gave up his reef aquarium on the urgent advice of his doctors. Unfortunately, the Palythoa polyps from his aquarium weren’t analyzed chemically or genetically.

To date, at least 100 people have been admitted to hospitals in Europe and North America after being poisoned by palytoxin from encrusting anemones in their aquariums via skin and/or eye contact or the inhalation of vapor (Pelin et al. 2016, Murphy & Charlton 2017). According to data from the National Poison Data System, in the United States alone there were 171 cases of poisoning in the 15 years between 2000 and 2014—116 through skin contact, 44 through inhalation, and 11 through a combination of both. In about one-third of these cases the result was hospitalization (Murphy & Charlton 2017). So far, no deaths from palytoxin poisoning have been documented in the scientific literature.

Dangerous vapor

Inhalation of the toxin causes severe symptoms of poisoning, including chest pain, fever, difficulty breathing, rapid heartbeat (tachycardia), and coughing. Vapor containing palytoxin can be generated when warm or hot water is poured onto Palythoa polyps or they are immersed in warm or hot water. In one case an aquarist attempted to clean Palythoa polyps from a piece of live rock by boiling the rock in water (Cortini et al. 2015). It is also possible to inhale poisonous vapor near a protein skimmer or airstone if injured or damaged Palythoa polyps are releasing secretions into the aquarium water.

In a case in Switzerland in 2012, three young men were seriously poisoned when they placed a piece of live rock containing Palythoa polyps in a newly set up aquarium before the marine salt had dissolved completely. Apparently, the water was still chemically aggressive and damaged the Palythoa polyps, causing them to release secretions containing palytoxin (Bernasconi et al. 2012)

There are also reports in the literature of parents and children being poisoned by the inhalation of vapor containing palytoxin from reef aquariums. The youngest patient was a two-month-old baby (Sud et al. 2013). In some cases the affected people suffered months of symptoms, such as difficulty breathing and weakness. One aquarist was unfit to work for three months due to such ailments (Wieringa et al. 2014).

Contact with skin and eyes

Palytoxin can enter the body through minor injuries to the skin or even through apparently intact skin (Deeds & Schwartz 2010, Nordt et al. 2011). Trying to clean a rock bearing encrusting anemones outside of the aquarium using a brush, toothbrush, or forceps may release a spray of secretion that gets directly into the eyes or can be introduced to an eye by a hand wetted with contaminated water. Numerous aquarists have reported that such incidents were followed by inflammation of the cornea and conjunctiva (keratoconjunctivitis), with temporary loss of vision in the affected eye (Knop 2000, Moshirfar et al. 2010, Ruiz et al. 2015).

Oral ingestion

The aquarium-hobby literature reports a number of cases of mild poisoning as a result of the toxin entering via the mouth. In all these cases the main symptom was an unusual metallic taste in the mouth. Friedrich (2012) reports that while he was scrubbing off a group of Palythoa polyps outside of the aquarium a spray of secretion from an encrusting anemone entered his slightly open mouth. He experienced the typical metallic taste and, a short time later, felt unwell and had tachycardia, circulatory problems, and a headache. The symptoms disappeared after a few hours with no further ill effects. There is also a risk of palytoxin poisoning via the mouth if the secretion-contaminated end of a siphon tube is placed in the mouth (Friedrich 2012). Accidental touching of the lips with a hand wetted with secretion has triggered similar symptoms and an unexplained feeling of being unwell.

Dangerous hidden passengers

Many Palythoa species live in shallow areas of the sea and can survive for hours out of water under the tropical sun when the tide goes out. Palythoa polyps are often introduced to the aquarium inadvertently as hidden passengers on live rock. In some tanks they then grow rapidly and reproduce, overwhelming stony corals and other sessile invertebrates. This is the way dangerous Palythoa species got into the aquarium in many of the cases of poisoning described in the medical literature (Deeds & Schwartz, 2010).

In the case of the aquarist in Bolzano, the poisonous Palythoa species had been inadvertently introduced to the aquarium on live rock two years previously. When the aquarist tried to scrub some of the Palythoa polyps from a rock under hot running tap water outside of the aquarium, he inhaled the resulting palytoxin vapor. The typical symptoms began two hours later: violent coughing, difficulty breathing, and raised body temperature. He had a high fever (>102.2°F/39°C), chest pains, and tachycardia and was taken to the respiratory intensive care unit at a hospital. He was released after six days, free of fever but still coughing (Tartaglione et al. 2016).

Dangerous encrusting anemone species

I preserved some of the Palythoa polyps from the aquarium of the Bolzano patient in 96 percent ethyl alcohol and sent them to Professor James Davis Reimer, an encrusting anemone specialist who works at the University of the Ryukyus in Okinawa, Japan. He identified them to species level (Palythoa cf. toxica) using genetic and morphological methods, and phylogenetic analysis showed that this species forms a closely related group of species with P. heliodiscus and P. variabilis. Given the cases of poisoning described in the scientific literature, all Palythoa encrusting anemones that exhibit similarities of form and color with these three species should be regarded as potentially very dangerous.

As part of a research project, 15 groups of encrusting anemone polyps (7x Palythoa and 8x Zoanthus), purchased in three different aquarium stores in Washington, DC, and the surrounding area, were analyzed (Deeds et al. 2011). Very dangerous amounts of palytoxin (500–3,500 µg/g) were found in four groups of Palythoa polyps, which genetic study showed were closely related to Palythoa heliodiscus. One P. mutuki and two from the genus Zoanthus were also classified as weakly poisonous. No palytoxins were found in the remaining colonies of polyps (two Palythoa and six Zoanthus). Using chemical analysis (liquid chromatography–high-resolution mass spectrometry, or LC-HRMS) and antibody-based testing procedures (enzyme-linked immunosorbent assay, or ELISA) the Palythoa cf. toxica polyps from Bolzano were found to contain palytoxins (palytoxin, hydrossypalytoxin, and desoxypalytoxin) totaling around 90 µg/g (Tartaglione et al. 2016). In addition to these P. cf. toxica polyps, the study included a number of polyps from the display aquarium at the South Tyrol Museum of Natural History in Bolzano, which were identified as P. mutuki using genetic and morphological methods. Only very small amounts of palytoxin were found in them.

Almost all documented cases of poisoning in the aquarium were caused by encrusting anemones of the genus Palythoa. In some cases there was no determination to species level, or the identification was suspect. It is almost impossible to identify Palythoa species on the basis of their form and coloration alone. In addition, the appearance of the polyps can alter during aquarium keeping. Put plainly, this means that at present we can distinguish between the very poisonous and the weakly poisonous or non-toxic species only by using complex laboratory analysis. Moreover, the systematics of the encrusting anemones are the subject of much dispute, as genetic research indicates that all Palythoa and Protopalythoa species belong to the genus Palythoa (Reimer et al. 2006). In other words, the genus Protopalythoa is no longer valid.

Palythoa polyps can still produce dangerous quantities of palytoxin even after several years in the aquarium. In some documented cases of poisoning the polyps had already spent two or three years in the reef aquarium (Deeds & Schwartz 2010, Tartaglione et al. 2016).

Detoxification with activated carbon

Daniel Knop (2012) reported that after reducing the number of Palythoa polyps in his 1,600-gallon (6,000-L) aquarium, he filtered the water through activated carbon in order to minimize palytoxin damage to fishes and corals. We wanted to find out whether activated carbon can actually remove palytoxin from the water, and if so, how effectively it does so.

In a laboratory at the Department of Pharmacy at the University of Naples Federico II, we filtered aquarium water containing a specific, known palytoxin concentration over aquarium-hobby pelleted activated carbon for 24 hours and then analyzed the water again. The results showed that 99.7 percent of the palytoxin in the water had been adsorbed by the activated carbon. We concluded that activated carbon is an effective means of minimizing these toxins in the water, but cannot eliminate them entirely (Tartaglione et al. 2016). But the experiment does show that using activated carbon in the reef aquarium can lower the risk of poisoning b contact with the water. (It does not, however, render living polyps themselves any less toxic.)

Protective measures

Aquarists who intentionally maintain Palythoa species or have inadvertently introduced them on live rock should take the following protective measures to minimize the risk of poisoning.

Wear protective gloves

Palytoxin can enter via small injuries or even through intact skin and is strongly dermotoxic (Deeds & Schwartz 2010, Nordt et al. 2011, Pelin et al. 2011). For this reason all Palythoa species (and, to be safe, Zoanthus species as well) should be treated as potentially poisonous and never touched with bare hands. If you must handle them, always wear heavy duty gloves made of latex or nitrile that are long enough to also protect the lower arms. Thin disposable gloves are less suitable, as they can tear easily if they come into contact with stony corals or sharp-edged rocks in the aquarium.

Wear a breathing mask and protective goggles

When working with Palythoa species, always wear a high-quality protective mask to avoid breathing vapor and protective goggles to keep secretion spray from touching your skin. If you don’t have any suitable protective goggles available, you can use a dive mask.

Avoid producing vapor

Never try to kill encrusting anemones with hot or boiling water, as that is guaranteed to release poisonous vapor. Numerous documented cases of poisoning were caused in this way.

Don’t scrub rock

Never try to remove encrusting anemones from substrate rock with a scrub brush or toothbrush. This can create a spray of poisonous secretions that can get in the mouth or eyes or be inhaled. Remember, even dead and dehydrated Palythoa polyps can contain palytoxin and are dangerous, even if they have been out of the aquarium for some time (Brockmann 2013).

Current wisdom dictates that you should proceed as follows when dealing with encrusting anemones:

• Switch off all pumps, protein skimmers, and any airstones in order to prevent the production of vapor.

• Ventilate the room (open windows).

• Put on protective gloves, protective goggles, and a breathing mask before removing pieces of rock on which encrusting anemones are growing from the aquarium.

• Because secretions from encrusting anemones may have been released into the aquarium water, filter the water over activated carbon for a number of hours before turning the current pump(s) and protein skimmer(s) back on.

• Keep other people (especially children and the elderly) and pets well away from the aquarium during the work.

Murphy, L.T. and N.P. Charlton. 2017. Prevalence and characteristics of inhalational and dermal palytoxin exposures reported to the National Poison Data System in the U.S. Environ Toxicol Pharmacol 55: 107–9.

I got another fifty of these from Singapore. Have two females and the rest males.Have one pairthat has fry. They have been very good parents but the growth rate of the fry has been the slowest of any apisto I have bred.They are two mos old and less than a quarter inch so no info yeton sex ratios

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